Production method for refined n-vinyl carboxylic acid amide

Abstract

[Problem] To provide a refinement method for producing refined N-vinyl carboxylic acid amides which is inexpensive and easy to manage. [Solution] A method of producing a refined N-vinyl carboxylic acid amide from a crude N-vinyl carboxylic acid amide, said method being characterized by including a base addition step and a distillation step, wherein a base is added to the crude N-vinyl carboxylic acid amide in the base addition step.

Description

Process for producing purified N-vinylcarboxylic acid amide

[0001] The present invention relates to a process for producing purified N-vinylcarboxylic acid amide.

[0002] N-vinylcarboxylic acid amide polymers derived from N-vinylcarboxylic acid amides are water-soluble polymers and dissolve not only in water but also in polar solvents such as alcohols and dimethyl sulfoxide (DMSO). Since they are nonionic polymers, they are not affected by salts or pH, and have high weather resistance, especially high stability against heat. Taking advantage of these properties, industrially, they are applied to binders, dispersants, adhesives, thickeners, flocculants, etc.

[0003] Many processes for producing N-vinylcarboxylic acid amide have been proposed so far. However, an additional step was required to remove N-butadienylacetamide, which is a polymerization inhibitor.

[0004] Patent Document 1 discloses a process for producing N-vinylcarboxylic acid amide, which comprises a step of controlling the content of unsaturated aldehydes in N-vinylcarboxylic acid amide to 20 ppm by mass or less.

[0005] Patent Document 2 discloses a process for producing high-purity N-vinylformamide, which comprises adding water and an aromatic hydrocarbon to crude N-vinylformamide containing formamide as an impurity and performing an extraction treatment to obtain an organic phase containing N-vinylformamide and an aqueous phase containing formamide, then separating the two phases, and then recovering N-vinylformamide from the organic phase.

[0006] Patent Document 3 discloses a process for producing a highly polymerizable N-vinylcarboxylic acid amide monomer, which comprises producing N-vinylcarboxylic acid amide by thermal decomposition or catalytic decomposition of crude N-(1-alkoxyethyl)carboxylic acid amide or crude ethylidenebiscarboxylic acid amide, and controlling the content of N-vinylcarboxylic acid amide in the crude N-(1-alkoxyethyl)carboxylic acid amide or crude ethylidenebiscarboxylic acid amide to 10% by mass or less.

[0007] International Publication No. 17 / 145569 JP 61-289069 JP 8-134029

[0008] However, the method described in Patent Document 1 uses a specialized thermal decomposition reaction in the synthesis of N-vinyl carboxylic acid amide, which involves equipment with high construction and operating costs. Furthermore, it was necessary to reduce the N-butadienylacetamide, a by-product of the synthesis, through a hydrogenation process using a precious metal catalyst. Moreover, these methods present significant management hurdles. The method described in Patent Document 2 uses aromatic hydrocarbons, making it difficult to adopt in modern times. The method described in Patent Document 3 requires a pressure crystallization process, which demands a large amount of thermal energy and results in significant capital investment. Furthermore, although N-vinyl carboxylic acid amide is recovered from the manufactured N-vinyl carboxylic acid amide synthesis solution by methods such as distillation, the decomposition of N-vinyl carboxylic acid amide due to heat during distillation remains a further challenge. The present invention was made to solve the above problems and aims to provide a purification method for producing purified N-vinyl carboxylic acid amide that is easy to manage and low-cost, even when the hydrogenation process is omitted and a general-purpose purification process is used.

[0009] The present invention includes the following embodiments: [1] A method for producing purified N-vinyl carboxylic acid amide from crude N-vinyl carboxylic acid amide, comprising a base addition step and a distillation step, wherein the base addition step is characterized by adding a base to the crude N-vinyl carboxylic acid amide. [2] The method for producing purified N-vinyl carboxylic acid amide according to [1], wherein the base used in the base addition step is at least one selected from lithium bicarbonate, lithium carbonate, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, cesium bicarbonate, and cesium carbonate. [3] The method for producing purified N-vinyl carboxylic acid amide according to [1] or [2], wherein the N-vinyl carboxylic acid amide is N-vinylacetamide. [4] The method for producing purified N-vinyl carboxylic acid amide according to [1] to [3], wherein an extraction step is included before the base addition step. [5] The method for producing purified N-vinyl carboxylic acid amide according to [1] to [4], wherein the temperature of the distillation step is 60°C or higher and 150°C or lower. [6] A method for producing the purified N-vinylcarboxylic acid amide of [1] to [5], wherein no polymerization inhibitor is added in the distillation step.

[0010] According to the present invention, by including a predetermined step, the decomposition of N-vinyl carboxylic acid amide in the distillation step is suppressed, and purified N-vinyl carboxylic acid amide with a low amount of N-butadienylacetamide can be produced using a general-purpose purification process, without employing steps such as hydrogenation, in an easy-to-manage and low-cost manner.

[0011] Embodiments of the present invention will be described in detail below. However, the present invention is not limited to the embodiments shown below.

[0012] The method for producing purified N-vinyl carboxylic acid amide according to this embodiment includes a base addition step and a distillation step. In this specification, "crude N-vinyl carboxylic acid amide" refers to a product containing components other than N-vinyl carboxylic acid amide in an amount of 20 to 60% by mass relative to the total amount of N-vinyl carboxylic acid amide. It may also be called a crude N-vinyl carboxylic acid amide composition because it contains other components. In this embodiment, a compound containing crude N-vinyl carboxylic acid amide can be purchased, or recycled materials can be used as crude N-vinyl carboxylic acid amide. Furthermore, it may be produced by going through the crude N-vinyl carboxylic acid amide synthesis step shown below before the base addition step, or by going through an extraction step.

[0013] <Synthesis Process> The synthesis process of the embodiments of the present invention is not particularly limited, but it is preferably a process of producing a compound containing crude N-vinyl carboxylic acid amide using a catalyst with carboxylic acid amide and vinyl acetate as raw materials. By using carboxylic acid amide and vinyl acetate as raw materials, the thermal decomposition process in the synthesis process can be omitted. Omitting the thermal decomposition process is preferable because it can reduce the construction and operating costs of the equipment. The carboxylic acid amide is not limited, but acetamide is preferred. The N-vinyl carboxylic acid amide in the crude N-vinyl carboxylic acid amide is not limited, but N-vinylacetamide is preferred. Acetamide and vinyl acetate are used as raw materials for N-vinylacetamide.

[0014] The vinyl acetate / carboxylic acid amide is not particularly limited, but a molar ratio of 0.5 to 10.0 is preferred, more preferably 1.0 to 5.0, and even more preferably 1.5 to 3.0. Within this range, the yield of crude N-vinylcarboxylic acid amide is sufficiently high, which is preferable.

[0015] The catalyst / carboxylic acid amide is not particularly limited, but is preferably 0.1 to 10.0 in molar ratio, more preferably 0.2 to 5.0, and even more preferably 0.4 to 3.0. Within this range, catalyst costs are kept down, which is preferable. The catalyst is not particularly limited, but is preferably an organic basic compound, more preferably dimethylaminopyridine, 1,8-diazabicyclo[5.4.0]undeca-7-ene, 1,5-diazabicyclo[4.3.0]-5-nonene, 1,1,3,3-tetramethylguanidine, and even more preferably dimethylaminopyridine. Dimethylaminopyridine is preferred because it is easy to recover and reuse.

[0016] A solvent may be used in the synthesis, but solvent-free is preferred because it allows for the omission of a solvent treatment step in the subsequent process. If a solvent is used, a polar solvent such as ethyl acetate is preferred. The carboxylic acid amide and catalyst may be present in the reaction vessel in their entirety from the start of the reaction, or they may be added sequentially to the reaction vessel by dropwise addition. The temperature of the synthesis process is not particularly limited, but is preferably 30°C to 150°C, more preferably 50°C to 120°C, and even more preferably 60°C to 90°C. The duration of the synthesis process is not particularly limited, but is preferably 4 hours to 50 hours, more preferably 6 hours to 30 hours, and even more preferably 8 hours to 24 hours.

[0017] <Low-Boiling Removal Step> In embodiments of the present invention, the low-boiling removal step may be used to remove low-boiling substances such as vinyl acetate that did not react in the synthesis step, and vinyl acetate and the like are recovered and used as raw materials. The temperature of the low-boiling removal step is not particularly limited, but is preferably 30°C to 90°C, more preferably 35°C to 80°C, and even more preferably 40°C to 70°C.

[0018] The pressure in the low-boiling removal process is not particularly limited, but is preferably 0.1 kPaA to 10 kPaA, more preferably 0.1 kPaA to 8 kPaA, and even more preferably 0.1 kPaA to 5 kPaA. The removal method is not limited, but can be simple distillation or continuous distillation.

[0019] <Extraction Step> In embodiments of the present invention, this step involves separating the composition containing the obtained crude N-vinylcarboxylic acid amide, which was acquired in the synthesis step, into the crude N-vinylcarboxylic acid amide and the catalyst using two types of immiscible solvents. The solvents are not particularly limited, but water and solvents immiscible with water are preferred. Examples of solvents immiscible with water include ethyl acetate, hexane, and toluene, with ethyl acetate being preferred.

[0020] In addition to the solvent, it is also preferable to add a salt. The salt is not particularly limited, but examples include sodium chloride, sodium carbonate, and sodium bicarbonate. For extraction, it is preferable to add a solvent that is immiscible with water to the aqueous layer 1 to 10 times and repeat the operation. In this operation, the crude N-vinyl carboxylic acid amide moves to the organic layer. The solvent may be removed from the organic layer as appropriate. The removal method is not particularly limited. After this, it is preferable to partially remove the solvent by simple distillation or the like. The crude N-vinyl carboxylic acid amide thus obtained contains carboxylic acids such as DAA (diacetamide) and acetic acid, and acetamide (AcNH ２ These include carboxylic acid amides such as ), EDA (ethanediol diacetate), etc. These are either reaction starting materials, by-products during the reaction, or generated when the product decomposes.

[0021] <Neutralization Extraction Step> In this embodiment, if necessary, the by-product acetic acid, etc., may be neutralized with a base to a neutral state before the extraction step described above. This is called the neutralization extraction step. The base used is the same as that used in the base addition step described later. Since this is neutralization, it is only to make the solution neutral, and it is distinguished from the base addition step described later, which makes the solution alkaline and performs a distillation step.

[0022] <Base Addition Step> The base addition step in this embodiment is a step of adding a base to crude N-vinyl carboxylic acid amide. The base can suppress the decomposition of N-vinyl carboxylic acid amide during heating. As the base, carbonates are preferred, more preferably lithium bicarbonate, lithium carbonate, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, cesium bicarbonate, cesium carbonate, and even more preferably sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate.

[0023] N-vinyl carboxylic acid amides tend to be hydrolyzed by acids such as acetic acid, but this can be suppressed by adding a base. The amount of base added is preferably 0.1 parts by mass to 20 parts by mass, more preferably 0.3 parts by mass to 10 parts by mass, and even more preferably 0.5 parts by mass to 8.0 parts by mass, per 100 parts by mass of the composition containing crude N-vinyl carboxylic acid amide.

[0024] <Distillation Process> In the distillation process of this embodiment, crude N-vinyl carboxylic acid amide is distilled. The distillation temperature is not limited, but is preferably 60°C to 150°C, more preferably 65°C to 130°C, and even more preferably 70°C to 110°C.

[0025] The distillation pressure is not limited, but is preferably 0.01 kPa or more and 3 kPa or less, more preferably 0.01 kPa or more and 2 kPa or less, and even more preferably 0.01 kPa or more and 1 kPa or less.

[0026] The distillation method is not limited, but examples include simple distillation and continuous distillation. The distillation method is not limited, but a method can also be used in which a liquid film of crude N-vinyl carboxylic acid amide is formed (under reduced pressure) and heated to leave behind and remove components with higher boiling points than N-vinyl carboxylic acid amide (hereinafter also referred to as the "thin film distillation method").

[0027] In the distillation process, it is preferable not to add polymerization inhibitors from the viewpoint of the stability of N-vinylcarboxylic acid amide and the effort required to remove the polymerization inhibitors. Examples of polymerization inhibitors include quinones, alkali-modified quinones, phenolic compounds, aromatic amine compounds, and thiourea compounds, as described in Japanese Patent Publication No. 3975525.

[0028] Amount of base added (Na, when the distillation raw material is 100 parts by mass) ２ CO ３ The amount of base added (in parts by mass) / distillation pressure (kPaA) at the start of distillation is preferably 0.5 or higher, more preferably 1.0 or higher, and even more preferably 2.0 or higher. If the amount of base added / pressure is 0.5 or higher, the amount of base will be sufficient to suppress the decomposition of N-vinyl carboxylic acid amide due to the amount of heat applied for distillation at that pressure, and as a result the decomposition of N-vinyl carboxylic acid amide can be suppressed, which is preferable. Amount of base added (when the distillation raw material is 100 parts by mass, Na ２ CO ３ The ratio of (parts by mass after conversion) to the distillation pressure at the start of distillation (kPaA) is preferably 50 or less for economic reasons related to the amount of base added. The base addition step and the distillation step may be performed multiple times.

[0029] <Crystallization Process> In the crystallization process according to the embodiment of the present invention, the crude N-vinylcarboxylic acid amide after the distillation process is crystallized. The crude N-vinylcarboxylic acid amide after the distillation process is dissolved in the presence of a crystallization solvent and a poor solvent, and then crystallized. The crude N-vinylcarboxylic acid amide monomer crystals after the crystallization process contain 88% by mass or more of the N-vinylcarboxylic acid amide monomer, preferably 90% by mass or more, and more preferably 92% by mass or more.

[0030] The crystallization solvent is not particularly limited, but at least one selected from acetonitrile, methyl ethyl ketone, toluene, ethyl acetate, and 1,2-dimethoxyethane is preferred. The mass of the crystallization solvent used is 0.01 to 0.5 in ratio to the mass of the N-vinylcarboxylic acid amide monomer crystals used, preferably 0.02 to 0.4, and more preferably 0.03 to 0.2.

[0031] Furthermore, while the poor solvent used is not particularly limited, aliphatic hydrocarbons having 6 to 7 carbon atoms are preferred. Preferred aliphatic hydrocarbons having 6 to 7 carbon atoms include n-hexane, cyclohexane, methylcyclohexane, n-heptane, and cycloheptane, with cyclohexane and methylcyclohexane being more preferred. Aliphatic hydrocarbons with 5 or fewer carbon atoms have low boiling points and are difficult to handle, while aliphatic hydrocarbons with 8 or more carbon atoms have high boiling points and may not be completely removed from the crystals. The mass of the aliphatic hydrocarbon having 6 to 7 carbon atoms is in a ratio of 0.5 to 3.0, preferably 0.5 to 2.0, relative to the mass of the N-vinylcarboxylic acid amide monomer crystals used. This ratio range is desirable because it allows for sufficient recrystallization of the N-vinylcarboxylic acid amide monomer, does not increase the amount of solvent used, and improves the volumetric efficiency of the crystallization apparatus.

[0032] The dissolution of N-vinylcarboxylic acid amide monomer crystals is not particularly limited as long as the temperature at which they can be dissolved in the solvent is within limits. The dissolution temperature for N-vinylcarboxylic acid amide monomer crystals is preferably 30 to 80°C, more preferably 30 to 60°C, and even more preferably 35 to 45°C. This temperature range is desirable because it allows the N-vinylcarboxylic acid amide to dissolve sufficiently without denaturation.

[0033] Next, the dissolved N-vinylcarboxylic acid amide monomer is cooled to precipitate recrystallization. The cooling temperature is preferably -20°C to 35°C, more preferably -15°C to 30°C, and even more preferably -10°C to 20°C. This temperature range is desirable because it keeps equipment costs low and provides a sufficient crystallization yield. The difference between the temperature at which the N-vinylcarboxylic acid amide monomer crystals are dissolved and the temperature at which the dissolved N-vinylcarboxylic acid amide monomer is cooled to precipitate recrystallization is preferably 1 to 100°C, more preferably 3 to 40°C, and even more preferably 15 to 30°C.

[0034] As an efficient method for separating the recrystallized N-vinylcarboxylic acid amide monomer precipitated in the crystallization process, separation by filtration is preferred. There are no restrictions on the filtration method, but from the viewpoint of separation from the crystallization mother liquor and productivity, centrifugal filtration or pressure filtration is preferred. Furthermore, rinsing after filtration is also preferred in order to improve the separation from the mother liquor. As the solvent used for rinsing, solvents selected from acetonitrile, methyl ethyl ketone, toluene, ethyl acetate, and 1,2-dimethoxyethane, and aliphatic hydrocarbons having 6 to 7 carbon atoms are preferred, similar to the crystallization solvent. The mass of the solvent selected from acetonitrile, methyl ethyl ketone, toluene, ethyl acetate, and 1,2-dimethoxyethane used for rinsing is preferably used in a ratio of 0.01 to 0.3, more preferably 0.01 to 0.2, and even more preferably 0.02 to 0.1, relative to the mass of the N-vinylcarboxylic acid amide monomer crystals recovered from distillation. Furthermore, the mass of the C6-C7 aliphatic hydrocarbon used in the rinsing process is preferably 0.1 to 3.0 in ratio to the mass of the N-vinylcarboxylic acid amide monomer crystals recovered from step (A), more preferably 0.1 to 2.0, and even more preferably 0.1 to 1.5. The crystallization step may be repeated multiple times.

[0035] The purified N-vinylcarboxylic acid amide obtained in the crystallization step preferably has an N-vinylcarboxylic acid amide concentration of 90% by mass or more, more preferably 93% by mass or more, and even more preferably 95% by mass or more. The purified N-vinylcarboxylic acid amide obtained in the crystallization step preferably has an N-butadienylacetamide content of 20 ppm by mass or less, more preferably 15 ppm by mass or less, and even more preferably 10 ppm by mass or less.

[0036] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

[0037] <Measurement of N-vinylcarboxylic acid amide concentration> The concentration was quantified by GC analysis under the following conditions. Instrument: High-performance general-purpose gas chromatograph "GC-2014" (Shimadzu Corporation) Column: DB-WAX (φ0.25 mm × 30 m, Agilent Technologies) Carrier gas type: He Carrier gas flow rate: 1 mL / min Split ratio: 40 Column temperature: The heating program was set in the following order: 40°C (7 min) → heating (25°C / min) → 130°C (15 min) → heating (30°C / min) → 220°C (7 min) Injection temperature: 200°C Detector: Flame ionization detector (FID) Detector temperature: 230°C Internal standard: Diethylene glycol dimethyl ether

[0038] <Measurement of N-1,3-butadienylacetamide content> The content was quantified by high-performance liquid column chromatography (HPLC) under the following conditions: Column: Shodex® SIL-5B manufactured by Resonaq Corporation; Eluent: Isopropyl alcohol (IPA) / N-hexane = 1 / 9 (mass ratio); Column temperature: 40°C; Flow rate: 1.0 mL / min; Detector: UV-Vis spectrometer, 254 nm

[0039] <Polymerization Test> The polymerizability of the obtained N-vinylcarboxylic acid amide is evaluated by the polymerization test described below. [1] Prepare a 100 ml glass container equipped with a catalyst injection tube, nitrogen blowing tube, nitrogen exhaust tube, and thermometer. [2] Weigh 20 g of N-vinylcarboxylic acid amide and 58 g of deionized water into the glass container from [1]. [3] Heat to 30°C in a water bath while bubbling with 50 ccm of nitrogen gas. Allow nitrogen gas to flow until polymerization is complete. [4] As a polymerization initiator, dissolve 1.6 g of V-044 (azoimidazoline type manufactured by Fujifilm Wako Pure Chemical Industries) in 48.4 g of deionized water. [5] As a polymerization initiator, dissolve 4.0 g of V-50 (azoamidine type manufactured by Fujifilm Wako Pure Chemical Industries) in 46.0 g of deionized water. [6] After 1 hour of nitrogen gas aeration, 1 g of polymerization initiator [4] is added, followed by 1 g of polymerization initiator [5] using a syringe. [7] The glass container is removed from the water bath, the moisture on the glass surface is removed with paper, and then it is transferred to an insulated container to continue polymerization. [8] The polymerization temperature is monitored, and the time to reach the standard temperature peak (time from the injection of polymerization initiator to reaching the temperature peak) from the addition of polymerization initiator [6] is used as an indicator of polymerizability. A good polymer was judged to have a standard temperature peak time of less than 120 minutes.

[0040] [Example 1] Crude N-vinylacetamide was synthesized by reacting 200 g of acetamide, 583 g of vinyl acetate, and 207 g of 4-dimethylaminopyridine at 70°C. Low-boiling components were removed from this synthesis solution at 60°C / 2 kPaA. Subsequently, the crude N-vinylacetamide after removal of low-boiling components was extracted with 990 g of ethyl acetate and 693 g of 7.5% by mass aqueous sodium carbonate solution. The aqueous layer was further washed with 594 g of ethyl acetate three times and 396 g of ethyl acetate once, and the ethyl acetate layers were washed together with 23% by mass sodium chloride + 2% by mass aqueous sodium carbonate solution. Then, ethyl acetate was removed by distillation at 40°C / 5 kPaA. 2.4 g of sodium carbonate was added to 237 g of the resulting crude N-vinylacetamide residue (N-vinylacetamide concentration 60.3% by mass) (base addition step), and 190 g of the NVA fraction was distilled off at 100°C / 0.1 kPaA (distillation step). The concentration of N-vinylacetamide in the obtained distillate was 69% by mass. The fraction was dissolved at 30°C with 113 g of methylcyclohexane and 10 g of ethyl acetate, cooled to -5°C for 7 hours, and crystallized. Solid-liquid separation was performed by centrifugation, and the mixture was further washed with 49 g of methylcyclohexane and 3 g of ethyl acetate. At this time, 81 g of N-vinylacetamide crystals were obtained, and the N-vinylacetamide concentration was 97%. The obtained crystals were dissolved again at 40°C with 85 g of methylcyclohexane and 15 g of ethyl acetate, cooled to 5°C for 7 hours, and crystallized. Solid-liquid separation was performed by centrifugation, and the mixture was further washed with 20 g of methylcyclohexane and 1 g of ethyl acetate. The obtained purified N-vinylacetamide crystals amounted to 71 g, with an N-vinylacetamide concentration of 99.9% and an N-butadienylacetamide content of 10 ppm or less. The polymerization test result for the obtained purified N-vinylacetamide was 105 minutes.

[0041] [Example 2] An extraction process was performed in the same manner as in Example 1, except that a 5% by mass aqueous sodium carbonate solution was used during extraction. After distilling off ethyl acetate, 187 g of a crude N-vinylacetamide solution (N-vinylacetamide concentration: 60.8%) was obtained. 1.9 g of sodium carbonate was added thereto (base addition step), and the same treatment as in Example 1 was performed except that the distillation was carried out at 120°C / 1 kPaA (distillation step), and 83 g of an N-vinylacetamide fraction was obtained. The N-vinylacetamide concentration in this distillate was 64.4% by mass.

[0042] [Example 3] 105 g of the residue after distilling off ethyl acetate obtained in the same manner as in Example 1 was separated (N-vinylacetamide concentration: 60.3% by mass). 1.1 g of sodium carbonate was added thereto, and the same evaporation treatment as in Example 1 was performed except that the distillation was carried out at 120°C / 1 kPaA, and 83 g of an N-vinylacetamide fraction was obtained. The N-vinylacetamide concentration in this distillate was 64.4% by mass.

[0043] [Example 4] 112 g of the residue after distilling off ethyl acetate obtained in the same manner as in Example 1 was separated (N-vinylacetamide concentration: 60.3%). 1.1 g of sodium carbonate was added thereto, and the same treatment as in Example 1 was performed except that the distillation was carried out at 130°C / 1.4 kPaA, and 86 g of an NVA fraction was obtained. The N-vinylacetamide concentration in this distillate was 62.9%.

[0044] [Example 5] 120 g of the residue after distilling off ethyl acetate obtained in the same manner as in Example 1 was separated (N-vinylacetamide concentration: 60.3% by mass). 3.6 g of sodium carbonate was added thereto, and the same treatment as in Example 1 was performed except that the distillation was carried out at 130°C / 1.4 kPaA, and 98 g of an NVA fraction was obtained. The N-vinylacetamide concentration in this distillate was 60.3% by mass.

[0045] [Example 6] 130 g of the residue after distilling off ethyl acetate obtained in the same manner as in Example 1 was separated (N-vinylacetamide concentration: 57.4% by mass). 6.5 g of sodium carbonate was added thereto, and the same treatment as in Example 1 was performed except that the distillation was carried out at 130°C / 1.4 kPaA, and 108 g of an N-vinylacetamide fraction was obtained. The N-vinylacetamide concentration in this distillate was 62.9% by mass.

[0046] [Example 7] 100 g of the residual liquid after ethyl acetate distillation, obtained in the same manner as in Example 1 (N-vinylacetamide concentration 60.3% by mass), was taken out and treated in the same manner as in Example 1, except that 4.8 g of sodium bicarbonate was added and the treatment was carried out at 130°C / 1.4 kPaA, to obtain 85 g of N-vinylacetamide fraction. The N-vinylacetamide concentration in this distillate was 67.6% by mass.

[0047] [Example 8] 100 g of the residual liquid after ethyl acetate distillation, obtained in the same manner as in Example 1 (N-vinylacetamide concentration 65% by mass), was taken and treated in the same manner as in Example 1, except that 7.9 g of sodium bicarbonate was added and the treatment was carried out at 130°C / 1.4 kPaA, to obtain 85 g of N-vinylacetamide fraction. The N-vinylacetamide concentration in this distillate was 68.4% by mass.

[0048] [Comparative Example 1] 130 g (N-vinylacetamide concentration 67.3% by mass) of the residue after ethyl acetate removal, obtained in the same manner as in Example 1, was subjected to the same procedure as in Example 1, except that it was distilled at 100°C / 0.2 kPaA without a base addition step, yielding 99 g of N-vinylacetamide fraction. The N-vinylacetamide concentration in this distillate was 76% by mass.

[0049] [Comparative Example 2] 140 g (N-vinylacetamide concentration 67.3% by mass) of the residue after ethyl acetate distillation, obtained in the same manner as in Example 1, was treated in the same manner as in Example 1, except that the base addition step was omitted and the treatment was carried out at 130°C / 1.4 kPaA, to obtain 40 g of N-vinylacetamide fraction. The N-vinylacetamide concentration in this distillate was 62.5% by mass.

[0050] NVA: N-vinylacetamide DAA: Diacetamide AcNH2: Acetate amide UK12.8: 1,1-Ethanediol acetate

Claims

1. A method for producing purified N-vinyl carboxylic acid amide from crude N-vinyl carboxylic acid amide, comprising a base addition step and a distillation step, wherein the base addition step is characterized by adding a base to the crude N-vinyl carboxylic acid amide.

2. The method for producing purified N-vinyl carboxylic acid amide according to claim 1, wherein the base used in the base addition step is at least one selected from lithium bicarbonate, lithium carbonate, sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, cesium bicarbonate, and cesium carbonate.

3. The method for producing a purified N-vinylcarboxylic acid amide according to claim 1, wherein the N-vinylcarboxylic acid amide is N-vinylacetamide.

4. A method for producing purified N-vinylcarboxylic acid amide according to claim 1, wherein an extraction step is included before the base addition step.

5. The method for producing purified N-vinylcarboxylic acid amide according to claim 1, wherein the temperature of the distillation step is 60°C or higher and 150°C or lower.

6. The method for producing purified N-vinylcarboxylic acid amide according to claim 1, wherein no polymerization inhibitor is added in the distillation step.

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